As a technique for extracting only a target audio source from different audio sources, there is a binary masking processing technique. The binary masking processing technique is to acquire audio with multiple microphones and separate the audio sources from one another based on the comparison of magnitudes of the audio acquired by the microphones.
In order to improve the accuracy of separating the audio sources, it is preferable to calibrate gains of the microphones before a process of separating the audio sources. For example, according to Japanese Laid-open Patent Publication No. 2007-129373, a calibration signal for gain adjustment is output from an audio source, the sensitivity of receiving the calibration signal by a standard microphone serving as a standard for the calibration is used as a standard value, and the sensitivity of receiving the calibration signal by another microphone to be calibrated is compared with the standard value. By generating calibration information of the microphones based on the result of the comparison, gains of the multiple microphones are adjusted.
Other examples of related art are International Publication Pamphlet No. WO2012/023268 and Japanese Laid-open Patent Publication No. 2005-077731.